Add smooth interpolation support for <color> custom properties

third_party/WebKit/Source/core/animation/CSSColorInterpolationType.h

Index: third_party/WebKit/Source/core/animation/CSSColorInterpolationType.h
diff --git a/third_party/WebKit/Source/core/animation/CSSColorInterpolationType.h b/third_party/WebKit/Source/core/animation/CSSColorInterpolationType.h
index 2d5c0eebfa90b5cdbf2f04a53c4c48972a120b1f..505e2013886e2cb250f0dea3207ee2020bb2b668 100644
--- a/third_party/WebKit/Source/core/animation/CSSColorInterpolationType.h
+++ b/third_party/WebKit/Source/core/animation/CSSColorInterpolationType.h
@@ -50,6 +50,10 @@ class CSSColorInterpolationType : public CSSInterpolationType {
                                        ConversionCheckers&) const final;
   InterpolationValue convertStyleColorPair(const StyleColor&,
                                            const StyleColor&) const;
+
+  const CSSValue* createCSSValue(const InterpolableValue&,
+                                 const NonInterpolableValue*,
+                                 const StyleResolverState&) const final;
 };
 
 }  // namespace blink